Cleanup stream_parser using some async_parser approaches

src/stream_parser.rs

@@ -1,24 +1,14 @@
-use bytes::{
-    Buf,
-    BufMut,
-    BytesMut
-};
-use futures::{
-    Async,
-    stream::Stream
-};
+use bytes::{Buf, BufMut, Bytes, BytesMut};
+use futures::{stream::Stream, Async};
 
-use crate::ebml::{
-    EbmlEventSource,
-    FromEbml
-};
+use crate::ebml::{EbmlEventSource, FromEbml};
 use crate::error::WebmetroError;
 
 pub struct EbmlStreamingParser<S> {
     stream: S,
     buffer: BytesMut,
     buffer_size_limit: Option<usize>,
-    last_read: usize
+    borrowed: Bytes,
 }
 
 impl<S> EbmlStreamingParser<S> {
@@ -31,13 +21,17 @@ impl<S> EbmlStreamingParser<S> {
     }
 }
 
-pub trait StreamEbml where Self: Sized + Stream, Self::Item: Buf {
+pub trait StreamEbml
+where
+    Self: Sized + Stream,
+    Self::Item: Buf,
+{
     fn parse_ebml(self) -> EbmlStreamingParser<Self> {
         EbmlStreamingParser {
             stream: self,
             buffer: BytesMut::new(),
             buffer_size_limit: None,
-            last_read: 0
+            borrowed: Bytes::new(),
         }
     }
 }
@@ -45,26 +39,23 @@ pub trait StreamEbml where Self: Sized + Stream, Self::Item: Buf {
 impl<I: Buf, S: Stream<Item = I, Error = WebmetroError>> StreamEbml for S {}
 
 impl<I: Buf, S: Stream<Item = I, Error = WebmetroError>> EbmlStreamingParser<S> {
-    pub fn poll_event<'a, T: FromEbml<'a>>(&'a mut self) -> Result<Async<Option<T>>, WebmetroError> {
-        // release buffer from previous event
-        self.buffer.advance(self.last_read);
-        self.last_read = 0;
-
+    pub fn poll_event<'a, T: FromEbml<'a>>(
+        &'a mut self,
+    ) -> Result<Async<Option<T>>, WebmetroError> {
         loop {
-            match T::check_space(&self.buffer) {
-                Ok(None) => {
+            match T::check_space(&self.buffer)? {
+                None => {
                     // need to refill buffer, below
-                },
-                other => return other.map_err(WebmetroError::from).and_then(move |_| {
-                    match T::decode_element(&self.buffer) {
-                        Err(err) => Err(err.into()),
-                        Ok(None) => panic!("Buffer was supposed to have enough data to parse element, somehow did not."),
-                        Ok(Some((element, element_size))) => {
-                            self.last_read = element_size;
-                            Ok(Async::Ready(Some(element)))
-                        }
-                    }
-                })
+                }
+                Some(info) => {
+                    let mut bytes = self.buffer.split_to(info.element_len).freeze();
+                    bytes.advance(info.body_offset);
+                    self.borrowed = bytes;
+                    return Ok(Async::Ready(Some(T::decode(
+                        info.element_id,
+                        &self.borrowed,
+                    )?)));
+                }
             }
 
             if let Some(limit) = self.buffer_size_limit {
@@ -73,19 +64,21 @@ impl<I: Buf, S: Stream<Item = I, Error = WebmetroError>> EbmlStreamingParser<S>
                 }
             }
 
-            match self.stream.poll() {
-                Ok(Async::Ready(Some(buf))) => {
+            match self.stream.poll()? {
+                Async::Ready(Some(buf)) => {
                     self.buffer.reserve(buf.remaining());
                     self.buffer.put(buf);
                     // ok can retry decoding now
-                },
-                other => return other.map(|async_status| async_status.map(|_| None))
+                }
+                other => return Ok(other.map(|_| None)),
             }
         }
     }
 }
 
-impl<I: Buf, S: Stream<Item = I, Error = WebmetroError>> EbmlEventSource for EbmlStreamingParser<S> {
+impl<I: Buf, S: Stream<Item = I, Error = WebmetroError>> EbmlEventSource
+    for EbmlStreamingParser<S>
+{
     type Error = WebmetroError;
 
     fn poll_event<'a, T: FromEbml<'a>>(&'a mut self) -> Result<Async<Option<T>>, WebmetroError> {